DWARF v5 source code embedding extension?

[Manouchehri]

Would be cool if we could embed the decompiled file into the output ELF. This is only supported as of DWARFv5 (I think it's backwards compatible with DWARFv4, so likely won't hurt).

Probably requires adding DW_LNCT_has_source and DW_LNCT_source to Ghidra first, not sure.

https://reviews.llvm.org/D42765

https://reviews.llvm.org/D42766